1. Field of the Invention
The present invention relates to an optical system for a camera and, more particularly, to an optical system for a camera in which an aperture stop is disposed between lenses and all lenses constituting the optical system are configured by aspheric plastic lenses.
2. Description of the Related Art
In recent years, as mobile communication devices such as a mobile communication terminal, a PDA, and a smart phone are increased in the quantity thereof and a service provided through a communication technology becomes various, various types of additional functions are provided in addition to a basic communication function.
Among them, a camera module is essentially mounted in the mobile communication devices for photographing or transmitting an image and video calling and various serves are provided by using an image photographed through a camera module or new services are being developed in close succession.
In particular, in recent years, a decrease in size, a decrease in weight, and a decrease in cost are required with respect to the optical system constituted by the lens group mounted on the camera module and a pixel size of an image sensor constituted by a CCD or a CMOS gradually decreases, a high-resolution optical system is required.
As such, a plurality of lenses are used for the optical system to maintain high resolution and the optical system is preferably configured by using a glass lens having high optical transmittance and a high refractive index, but the optical system mounted in the mobile communication device is difficult to satisfy conditions of the decrease in size and the decrease in cost as a design of the optical system by characteristics of the optical system.
Therefore, the optical system mounted in the mobile communication device uses a plastic lens which can be easily molded and reduces the number of lenses as possible in order to decrease the size and save manufacturing cost, but the optical system uses a plastic lens having deteriorated optical performance in comparison with the glass lens, it is difficult to satisfy the optical performance by designing the optical system and design flexibility of the optical system is deteriorated due to the decrease in number of lenses.
Meanwhile, as the general design of the optical system, a design method in which an aperture stop is positioned at the forefront of each of the plurality of lenses and the plurality of lenses are arranged in sequence is adopted, but in this case, many aberrations are induced by light passing through an end of the aperture stop.
Further, when the aperture stop positioned at the forefront of the optical system is away from a first lens adjacent to an object, the size of the first lens increase and the length of the optical system increases, thereby remarkably deteriorating the optical performance.